Incorrect billing system

I was billed a very high usage which i argue to be incorrect. My normal range of usage is 3-4 units daily and 8-10 units if I use the washing machine. I was billed a usage of 19 units which doesn't make sense as I never use that much electricity in a normal day. I called and the lady by the name of Rose told me there's nothing myvoltage could do to either rectify or investigate this error. How do I now as a customer sit with an unresolved query because im told nothing can be done but I am also billed incorrectly